This invention relates to electro-optical systems, and particularly to electro-optical systems for flying spot television scanner apparatus.
A flying spot television scanner apparatus typically comprises a film transport mechanism including a driven take-up spool and a driven intermittent drive mechanism. Electric motors are provided for driving the take-up spool and the intermittent drive mechanism, and these motors are so controlled as to ensure that a film passes through a film gate in the transport mechanism at a rate of film frames per second which preserves the illusion of natural motion on the film and also enables each frame of the film to be scanned by two or more television scanning fields while ensuring that pull-down of the film between successive frames presented for scanning in the gate occurs only during a field blanking pulse of the television scanning. The scanning is accomplished by a point of light carrying out a television field scan on the picture area of a film frame in the gate. This point of light is produced by a cathode ray tude combined in the flying spot scanner apparatus with an optical system arranged to project an image of a faster area of the screen of the cathode ray tube onto the picture area in the gate. The cathode ray tube is coupled to television scanning and blanking circuits which in operation produce a television raster on the raster area of the tube screen.
For color television, the light from the scanned film must be separated into red, green, and blue components centered on predetermined wavelengths prescribed by standards accepted for color television.
This separation is, in known flying spot scanners, typically achieved by the use of two dichroic mirrors and a respective trimming filter for each separated color. Such an arrangement is described at pages 139 to 143 of "Principles of PAL Color Television and Related Systems" by H. V. Sims, 1969, published by Iliffe Books, Butterworth & Co. (Publishers) Ltd., London. The separated light is sensed by three photomultipliers, one for the red light, one for the green, and one for the blue.